Recently, liquid crystal projectors and liquid crystal projection TVs, in which an image on a liquid crystal panel is projected onto a screen by a magnifying optical projection system utilizing a liquid crystal display (LCD) panel as an optical switching element, have been become popular. These devices are advantageous in that they are thin and lightweight, have sharp images, are not affected by earth's magnetic field, and do not require registration adjustment.
Projection televisions are known to include front and rear projection arrangements. Generally, but not exclusively, the front projection televisions are arranged to project the image on to a separate screen, whereas for rear projection televisions, the image is projected from behind a viewing side of the screen, which forms an integral part of the television.
LCD rear-projection TVs are often classified into single-panel systems composed of a liquid crystal panel having color filters for three colors, i. e., B (blue), R (red), and G (green), and three-panel systems having monochrome liquid crystal panels for the B, R, and G optical paths. According to the single-panel systems, a compact and lightweight liquid crystal device can be readily formed at a lower cost because of its simple structure. However, since the color filters absorb a large amount of light, it is difficult to achieve higher luminance and efficient cooling.
One problem that sometimes arises in LCD rear-projection TVs is that the picture appearing on the display can be misoriented and thus become distorted as a result of external mechanical influences such as shock and vibration that occurs during shipping. Such external influences can cause the optical projection unit to shift in position relative the other optical elements that are employed such as the various lens assemblies, mirrors and screen. Moreover, in addition to misorientations that arise during shipping, the correct position of the projection unit relative to these other optical elements can be difficult to achieve with complete accuracy when the TV's are manufactured in a mass-production environment.
Accordingly, it would be desirable to provide a method and apparatus for automatically correcting image misalignment that may arise in an LCD rear-projection television display.